Fluid systems serving, for example, a lubricating function in mechanical power transmitting systems become contaminated by wear particles from the various components of the mechanical system. For example, bearings and gears are known to spall and to produce so-called "debris" which enters the fluid system.
It is known to utilize this phenomenon of wear particles as a means of detecting the integrity of the mechanical system. Detection is achieved by monitoring the fluid system.
One such apparatus is described in U.S. Pat. No. 3,878,103 and a related apparatus is disclosed in U.S. Pat. No. 3,686,926. Both patents describe an apparatus for detecting debris in the fluid of hydraulic, lubricating, or cooling systems, for instance. These apparatuses comprise a sensor housing and a woven mesh screen within the housing. The fluid of the system enters the sensor housing and flows through the screen. The screen comprises a pair of electrical conductors of opposite polarity and a non-conductive wire woven with the electrical conductors. The debris, such as metal spall flakes or chips from a transmission bathed in the fluid of the system, contacts the pair of conductors and completes an electrical circuit. The apparatus is responsive to electrical conductivity that occurs between the pair of conductors and through the spall flake or chip, and produces a signal indicating the presence of the spall flake or chip. The apparatus includes a pressure sensor that indicates the accumulation of debris on the screen.
Though the pressure sensor indicates accumulation of debris, the pressure sensor of the noted patents does not indicate sufficiently small uniform increments of the accumulation of debris. Since the presence of small amounts of debris in the fluid is not always detectable, the time period in which a threshold amount of debris accumulates before that amount can be detected by the pressure sensor, is not always sufficient. Furthermore, the limited number of electrical circuits available in the screen would prevent an accurate measurement of debris accumulation using this conductivity technique.